Hand in hand with the expansion of the camera phone market including the market for smart phones, digital camcorders, digital cameras and the like, there have been advancements in techniques for photographing pictures or moving images. One of those is a technique for recognizing a face of a person in an image photographed using a digital image pickup device so as to automatically focus on the face or automatically photograph the person when the person makes a specific facial expression.
However, in an ordinary environment, images of faces photographed from diverse angles, various facial expressions, and lighting (natural light, artificial light or the like) from various directions are the causes for degradation of performance in recognizing the face. In an effort to overcome the above difficulties, in cases where basic reference facial images for face recognition are registered in a database, an improvement in performance can be obtained by pre-registering as many diverse facial images as possible. However, since memory resources of the digital image pickup device such as a digital camera or a camera phone are limited, there is a problem of not having enough resources to store all of the available facial images.
Accordingly, there is a need for an efficient method of selecting and registering, among newly photographed or input facial images, facial images that would effectively improve performance of face recognition operations and deleting some of the previously stored facial images in view of the limited memory resources.